When it is stated that between two and five years the change from temporary to permanent teeth is effected in regard to twenty-four temporary teeth, it will be apparent that the process is conducted with considerable rapidity; in fact, a large instalment of the total takes place during the third year of the animal's life, in which period four incisors and eight molar teeth are changed for permanent teeth.

Soon after two years the red and depressed condition of the gum round the upper central temporary incisors indicates that the teeth are being pushed out of their place by the permanents growing underneath them. These signs are quickly followed by similar signs in the lower temporary incisors, and by two years and a half the four permanent organs are usually cut, and the mouth presents a very peculiar and characteristic appearance. At three years old the four incisors are usually fully developed, as shown by the wear of the anterior edge, which is well marked in the drawing below (fig. 609).